internal server error (500) on using API

Hi , my code in c# is :

string fdDomain = "mycompany";

string apiKey = "x0x0x0x0x0x0x0x0x0";

string apiPath = "/helpdesk/tickets.json";

string json = "{\"status\": 2, \"priority\": 1, \"email\":\"test@test.com\",\"subject\":\"test\",\"description\":\"confirm whether received\"}";

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://" + fdDomain + ".freshservice.com" + apiPath);

request.ContentType = "application/json";

request.Method = "POST";

byte[] byteArray = Encoding.UTF8.GetBytes(json);

request.ContentLength = byteArray.Length;

string authInfo = apiKey + ":X"; // It could be your username:password also.

authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo));

request.Headers["Authorization"] = "Basic " + authInfo;

//ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(ValidateServerCertificate);

Stream dataStream = request.GetRequestStream();

dataStream.Write(byteArray, 0, byteArray.Length);

dataStream.Close();

try

{

WebResponse response = request.GetResponse();

dataStream = response.GetResponseStream();

StreamReader reader = new StreamReader(dataStream);

string Response = reader.ReadToEnd();

return Json(Response);

The message erro is "Server internal erro (500)",

Thanks